Thermostatic control switch



April 14, 1953 T. N. FLIGHT ET AL 2,635,157 THERMOSTATIC CONTROL SWITCH Filed May 2, 1950 4 Sheets-Sheet l venTZms A ril 14, 1953 T. N. FLIGHT ET AL 2,635,157

THERMOSTATIC CONTROL SWITCH Filed May 2, 1950 4 Sheets-Sheet 2 FIG. 2.

April 1953 T. N. FLIGHT ETAL 2,635,157

THERMOSTATIC CONTROL SWITCH Filed May 2, 1950 4 Sheets-Sheet 3 Ap 1953 T. N. FLIGHT ETAL 2,635,157

THERMOSTATIC CONTROL SWITCH Filed May 2, 1950 4 Sheets-Sheet 4 Gr! 45 44 i i FIG-4.

RMs-ys Patented Apr. 14, 1953 UNITED STATES PATENT OFFICE 2,635,157 THERMOSTATIC CONTROL SWITCH Theodore N. Flight, Farnham Common, William -H. Wilson, Camberley, and Arthur J. Chinn, Slough, England, assignors to The Rheostatic Company Limited, Slough, England Application May 2,1950, Serial No. 159,612

' In Great Britain May 3, i949 This invention relates to thermostats for controlling the temperature of electric ovens or the 3 Claims. (Cl. 200-140)- like in which at least one of the thermally ac- As disclosed in the specification of. applica- I tion No. 39,276 the magnetic snap actionswitch of this invention consists of a resilient switch member carrying two iron armatures positioned one on each side of a permanent magnet, and so adjusted for movement that one armature remains closer to the magnet than the other in both the open and closed positions of the switch. This adjustment of armatures produces a magnetic bias acting as a closing force between switch contacts, one of which is carried by the resilient switch member, the co-acting contact being :arranged with screw adjustment in a supporting plate.

By the use of this arrangement of magnet and twin armatures the force needed for switch operation is limited to the adjusted diiierence in pull of the magnet on the two armatures which force can be of such low value relative to the strength of the resilient switch member that consistent and reliable action can be obtained within a switch head of minimum dimensions.

In some types of electric oven it is inconvenient to arrange the adjusting means for a controlling thermostat switch adjacent the thermal member of the thermostat in the oven.

It is therefore common to arrange the thermal member as a phial connected by capillary tubing with an expansible chamber within the switch head which is mounted in a convenient position tor manual operation, the phial tubing and expansible chamber being hermetically sealed after filling with a thermo sensitive liquid which will not boil at the highest temperatures encountered in such ovens.

This invention uses such a thermo-sensitive system the expansible chamber being either a bellows or diaphragm unit fixed with adjustment means relative to the switch base and being connected for operation of the switch with the end of a setting adjustment screw.

The end of the adjusting screw remote from the base presses on the moving portion of the expansible bellows or diaphragm. The adjusting screw is therefore subject to movements oi the thermal element operating member and transmits these movements to the resilient switch lever to open the switch with increasing tem- Y 2 perature in the thermo phial system.

The calibration of the thermostat is accomplished by the adjustment of the position of the expansible unit relative to the supporting base.

A limited adjustment of this calibration is also provided to enable small variation in the calibration of an'individual instrument to be made to suit the thermal characteristics of a particular oven.

This adjustment is in the form of a screwed nut supported by and rotating in a rigid frame attached to the switch base and carrying the screwed stem of the expansible element so as to raise or lower the expansible unit relative to the adjusting screw and switch.

In some domestic electric ovens the heating elements are divided into two groups. When the oven is heating up from cold both sets of elements are energised but once up to temperature only one set of elements is used, the pre-set temperature being maintained by the thermostat switch controlling On and Oii this one set of heaters.

This invention provides for the control of such ovens by the provision within the switch head of a second switch, to control the preheat elements which switch may be either of a nonaccelerated slow break type or of the snap-action type already described in co-pending application No. 39,276.

This switch A controlling the preheat elements supports the adjusting screw in its insulating block carrier and is mounted on the same support rods above the first mentioned quick make and break switch B which controls the temperature maintaining elements.

Between switch A and switch B is mounted a second insulating block contacting the underside of switch lever A and resting on the top of switch lever B.

Movement of the adjusting screw towards the switch base with rising temperature or manual adjustment of the temperature setting knob to a lower temperature will therefore press on both switches A and B.

It is then provided by the adjustment of switch A that is will open circuit to interrupt the preheat elements at a slightly lower temperature in the oven than that set for opening the controlling switch B and in normal operation will not reclose to re-energise the preheat elements unless the oven temperature falls to a figure well below the thermostat setting or the thermostat setting be raised to a higher figure.

It is also provided that thi pre-heat switch sensitive liquid filling the can, if required, be arranged to be held in open position once it has been tripped until reset mechanically by the manual operation of the setting knob.

In this embodiment of the invention the resilient switch "lever fo'f the :prehea't switch is provided with an armature at its contact :end and a permanent magnet supported in a plate held in the switch pack is arranged to retain the switch A hole in the closed end of the U frame allows the insertion of a capsule ll attached to the carrying plate l8 which in turn is screwed to the U frame as shown.

The capsule l1 consists of two corrugated discs soldered together around their gperiph'ery. One disc carries the cup 40 in which .a'bimetal disc [9 and a plate disc 29 are located. The other .n'orrugated disc is attached to a screwed stem 4| in open position by the attraction between .the 10 which .ispierced .axially and forms the connecarmature and the permanent magnet.

With this arrangement the ,tpreheat :switch is closed by a cam acting from the temperature setting knob spindle releasingthe armature from attraction by th permanent magnet andclosing the switch contacts. I

Alternatively the preheat switch mayhe bia'sed to the contacts-open position to be closed mechanically by the cam on the manual operating knob spindle, held closed by magnetic cling and released by thermal :movement with :rising oventemperature to remain open unless reclosed again by-manualoperation.

It .is also arranged that in the positionof the setting knob foruclosure of this preheat element switch the circuit of the maintemperaturefmaintaining'element is-held open.

If the preheat element be arranged in the top of the oven it can then be used for-grilling or toasting in this position of the switch.

Rotation of the setting :knob away from this grill position :allowsclosure-of the temperature maintaining or baking element circuit.

Rising temperature in the oven will thencpen first the preheat element circuit which circuit will then be held open by the :magnetic clingon its switch and at the temperature of the knob setting the bake -or temperature maintaining circuit will :be opened to be :closed and -.opened again under the control .of the thermostatic switch to maintain the temperaturepfits setting.

This invention is illustrated in thezaccompa-nying drawings .in which :Figure .1 is an elevation of a thermostat constructed in accordance with this invention the terminal panel being removed to show the-switch. Figurez .is .an elevation .in section of another embodiment in whicha second snap .action switch to control the -prehea-t element is incorporated in the switch .-pack. Figure 3 shows the arrangement of auxiliaryswitch to open the bake element circuit while leaving the other switch under thermostatic control in thefgrill position iof the setting Lkn'ob. 'li igure shows the electrical connections of 'thefsviitches provided to accomplish this purpose. The reference numerals used in'Figure tare those applied to the switch elements Shownlin'FiguresIZ and S.

Referring to the drawings, the switch supporting frame I carries a pair .of tie-rods .2, F3, .on which the magnetic snap action switch v.is clamped.

Insulating bushes H, L? are interposed between the various components which comprise: magnet 4 in its supporting plate 5, a spring switch .lever B carrying one contact 7 and a twin armature unit 8, the second contact 9 being carried .in plate it.

The position .of the twin armature unit relative to the magnet is set by the screw adjustment-of contact 9 and the extent of the switch opening movement is limited by the bending of a tongue l 3.

The switch case consists of a U shaped metal pressing it to the open end of which the base l5 and fixing bush l6 are attached.

tion'ifrom the 'space between the capsule and capillary tube 2| to the Opposite end of w ich tube :aatherma lly:sensitive1phial 22 is fixed.

:Calibration adjustment is provided by nut 24 ;supporting.thecapsu1e by the threaded engage ment with stemt! and resting on plate I8 under pressure .oia .springzs 'The'kndbZS is provided for setting the operat- ;ing temperature of the thermostat and is carried by a spindle 26 the forked end of which engages with .a pin .21 across the end of an adjustin screw .28.

This .screw 23 is .in threaded engagement with -.a nut 29 l'held against .rotation .in a rectangular insulation block 39. This block =30 is in turn held against rotary movement in .plate 10. The block 3!! is supported by resting'on Lthe springswitch lever "E the'bottom of the block 313 beingformed to give line contact with the switch lever .as

:shown at 3 I.

The adjusting screw '28 .is hollow and carries a pin -'32 held with .a pro-determined loading by .a spring 33 to receivepressureand movement from the downward movement of the diaphragm 1 7 withthe increase of temperature .on thephial'Z Z.

This downward movement produces pressure between block 39 and switch'leverlt to open the switch contacts ll, 9, with increasing tempera- Thermal expansion continuing after the ture. opening of the switch will give increased pressure on the'switch lever but thisincrease is limited to the pro-sent value or the pressure of the spring 33 which beyond its set pressure Jfigure allows In Figure 2 is also shown'the second snap'action-switch which may beem'bodied in this'thermostat to give separate 'ccntrol'to a preheat elementin theoven.

This switch is similar to the switch already describedand consists of a magnet .42 initssupporting plate at, switch -arm 44 carrying one contact 4'5 andtwin armature unit '45. The second contract of the switch is shown'at '41, being carried in the supporting plate 48. This plate 48 embraces and holds against rotation the insulating block "t9 which rests on switch lever 44 at 5| as shown.

Within this block and'threaded on the :adjusting screw 28is a second adjusting nut 50.

In operation, with increasing temperature on the thermally sensitive phial the adjusting nut 58 presses through block '49 to open the switch contacts i5, 41, with downward movement to the adjusting screw.

The nut 29 also exerts an opening force through the block .30 on the switchlever 6 to open the contacts 1,19.

The temperature interval between which these two openingmovements take placeis set by the screw adjustment of the nut50 relative to the nut-29 .on the screw 28.

The nut 50 is then held against accidental rotation by friction grip in the block 49 so that the temperature interval between the operation of the two switches is held constant for all settings of screw 28 relative to-the thermal actuator ll. if

In order that on certain types of cookers the grill" or pro-heat element may be used without the bake element for grilling, a separate switch is provided the blades 36, 31 of which when joined give connection from the main supply lead to the bake" element thermostatic switch. The rotation of the knob 25 to the grill position brings the cam tongue 38 of the washer 58 which is rotated with the spindle 26 in position to lift the lever 39 and separate the contact strips 38, 31 thus isolating the bake element in this position.

In order that on certain types of cookers the grill or preheat element may be used without the bake" element for grilling it is necessary that the bake element be disconnected in the grill only position of the setting knob 25.

In Figure 4 illustrating the electrical connections of the switches provided to accomplish this purpose 56 and 51 indicate the incoming mains, one of which is connected to the junctions of switch members 31 and 41. Switch arm 44 and contacts 45 and 41 form the thermally operated switch in the circuit of the grill or preheat" element 52, and switch lever 6 and contacts I, 3

form the thermally operated switch in the circuit of the bake element 53. The other supply main is connected to the opposite sides of the elements 52 and 53.

The switch comprising blades 36 and 31 is interposed between the incoming supply main 56 and the bake switch comprising members 8, 1, and 9.

The mechanical disposition of switch 36-31 is shown in Figure 3 in which strip 31 is clamped in below switch blade 44, the strip 31 carrying at its end remote from its clamping a contact 54 co-acting with a second contact, on 36 carried by a support bracket clamped with contact plate [0, Figure 2 (not visible in Figure 3).

The spring lever 39 carries a vertical push rod 55. A washer 58 mounted on and rotating with the adjusting spindle 28 carries a tongue 38 which lifts push rod 55 to separate contact blades 36 and 31 in the grill only" position of the knob 25 when tongue 38 is turned to engage a projection 59 on spring lever 33 and lift this lever and rod 55.

What we claim is:

1. In a thermostatic electric switch including a. thermostatic means responsive to temperature changes, an adjusting dial for adjusting the thermostatic means to respond to the desired temperature, an externally threaded screw mounted endwise between the thermostatic means and the dial and rotatable by the dial, said screw being provided with an axial bore, a pin slidably mounted in the end of the bore adjacent to the thermostatic means and in operative relation thereto, a spring mounted in said bore biasing said pin towards the thermostatic means, a nut threaded on said screw, a block of insulating being movable along the screw when the latter is rotated, and an electric switch including a spring switch lever engaged by said block and movable thereby to open the switch, said screw and block being movable axially by the thermostatic means to actuate said lever in a direction to open the switch.

2. A thermostatic electric switch as claimed in claim 1, including a mounting for the thermostatic means which comprises a threaded shaft on which the thermostatic means is carried, and a nut on the shaft for controlling the position of the thermostatic means relative to that of the adjusting screw and thereby adjusting its calibration.

3. An electric thermostat comprising a switch base, a case attached to the base, a magnetic snap-action switch having a spring switch lever carrying one contact of the switch and a twin armature unit embracing a permanent magnet carried by a supporting plate all mounted in said case, a second contact arranged with screw adjustment in a carrying plate all with insulation forming a switch pack which is supported on a pair of tie-rods extending from the switch base. an expansible capsule supported by the case, a liquid-filled phial connected by a capillary tube to the capsule, means for adjusting the initial position of the capsule with respect to the case, said adjusting means including a nut mounted on the case and a stem threaded in the nut and carrying the capsule, said threaded stem forming part of the capillary tube, an adjusting screw, a nut threaded on the adjusting screw and held against rotation in an insulating block supported by the spring switch lever, a temperature-setting knob, one end of the adjusting screw engaging for rotation with the temperature-setting knob, the other end of the adjusting screw being provided with an axial bore, a pin mounted in the bore adjacent the capsule and in operative relation thereto, and a spring in said bore biasing said pin towards the capsule, said pin receiving pressure from the expansible capsule to move the adjusting screw and block to in turn press open the switch with increasing temperature on the phial.

THEODORE N. FLIGHT. WILLIAM H. WILSON. ARTHUR J. CHINN.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 983,976 Carpenter Feb. 14, 1911 2,184,339 Ettinger Dec. 26, 1939 2,197,230 Waddell Apr. 16, 1940 2,291,501 Persons July 28, 1942 2,314,989 Kercher Mar. 30, 1943 FOREIGN PATENTS Number Country Date 939,614 France Apr. 26, 1948 

